Core-free thermoplastic polyurethane yarn formed with resin and method for producing same

ABSTRACT

The present invention relates to a resin for a thermoplastic polyurethane yarn, comprising: thermoplastic polyurethane; and silica nanopowder. The present invention also relates to a method for producing a thermoplastic polymer yarn having a thickness of 50 denier or less by use of silica nanopowder having a particle size of 5-30 nm as a thickener. The thermoplastic polyurethane resin according to the present invention has desired processability and physical properties.

REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of pending U.S. patent application Ser.No. 15/190,503 filed on Jun. 23, 2016, and claims priority of KoreanPatent Application No. 10-2016-138458 filed on Oct. 24, 2016, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a resin for a thermoplasticpolyurethane resin, which comprises silica nanopowder, and a method forproducing a thermoplastic polyurethane yarn using the resin. Morespecifically, the present invention relates to resin for a thermoplasticpolyurethane (TPU) yarn, which comprises silica nanopowder that makes itpossible to continuously produce a TPU yarn having a diameter of 50denier or less without causing yarn breakage, and to a method forproducing a thermoplastic polyurethane resin using the resin.

BACKGROUND OF THE INVENTION

As is well known in the art, yarns which are used for industrialapplications or as materials for shoe uppers are generally made ofpolyester, nylon, acrylic resin or the like. Fabrics made of such yarnshave insufficient durability and abrasion resistance and also problemsin terms of adhesive strength and the like, and for this reason, the useof such yarns for high-functionality applications is not suitable.

To solve such problems and increase the strength of yarns, coated yarnsobtained by coating the surface of yarns with thermoplastic resins arecurrently being used. Such coated yarns are generally produced bycoating yarns (such as polyester or nylon yarns) with thermoplasticresin such as polyvinyl chloride (PVC), polypropylene (PP) orthermoplastic polyurethane in the dice of a conventional extruder.

However, where conventional thermoplastic resin as described above isused, there are disadvantages in that it is difficult to control theamount of coating with this thermoplastic resin, and particularly, it isdifficult to apply this thermoplastic resin in small amounts, and thusthe use of this resin can provide only coated yarns having a thicknessof 300 denier or more, which also have poor durability or abrasionresistance.

In order to solve such problems, up to date since 2012, the presentinventor has conducted studies on a method for production of a coatedyarn, a compound for a coated yarn, a thermoplastic polyurethane-coatedyarn, etc. (see Patent Documents 1 to 4 below).

The inventions disclosed in such Patent Documents make it possible toproduce a coated yarn not only exhibiting excellent abrasion resistance,adhesive strength, waterproof ability and moldability, but also having arelatively thin thickness. However, in the case of coated yarns having acore formed of polyester or nylon, there is a limit to reducing thethickness of the coated yarn, and thus it is impossible to produce acoated yarn having a very thin thickness, preferably a thickness of 50denier or less.

In addition, in the case of a thermoplastic polyurethane yarn(TPU)-coated yarn disclosed in the prior art patent documents, athickener is necessarily required for smooth extrusion, because thethermoplastic polyurethane has a lower viscosity than polyester ornylon.

Unlike the TPU-coated yarn, an uncoated yarn such as a mono-filamentyarn having a large thickness can be produced using silica having ageneral size as a thickener. However, in the case of a mono-filamentyarn or multi-filament yarn having a small thickness, particularly athickness of 50 denier or less, general silica powder cannot be applied,because the yarn should be produced to have a small thickness.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the problems ofthe thermoplastic polyurethane-coated yarns disclosed in theabove-described prior art patent documents, and it is an object of thepresent invention to provide a resin for a thermoplastic polyurethane(TPU) yarn, which comprises silica nanopowder as a thickener suitablefor producing a core-yarn TPU yarn having a small thickness so as toexhibit desired processability and physical properties, and a method forproducing a thermoplastic polyurethane (TPU) yarn using the resin.

Another object of the present invention is to provide a resin for athermoplastic polyurethane yarn, which comprises silica nanopowder thatmakes it possible to produce a thermoplastic polyurethane (TPU) yarnhaving a thickness of 50 denier or less, and a method for producing athermoplastic polyurethane yarn using the resin.

To achieve the above object, the present invention provides a resin fora thermoplastic polyurethane yarn, comprising: thermoplasticpolyurethane; and silica nanopowder having a particle size of 30 nm orless, preferably 5-30 nm.

The present invention also provides a method for producing athermoplastic polyurethane yarn using the above-described resin, themethod comprising the steps of: (1) preparing liquid raw materials,which comprise polyol, isocyanate and short-chain glycol, respectively,and are used for preparation of thermoplastic polyurethane (TPU) polymerpellets, and selecting any one selected from among the liquid rawmaterials, and adding and compounding silica nanopowder having aparticle size of 30 nm or less into the selected liquid raw material;(2) simultaneously introducing the silica nanopowder-dispersed liquidraw material of step (1) and the remaining two raw materials into areaction-type extruder to form TPU polymer pellets to thereby produce aresin for a TPU yarn; and (3) introducing the resin for the TPU yarninto a yarn extruder, and melt-extruding the introduced resin throughthe yarn extruder, thereby producing a thermoplastic polyurethane yarnhaving a thickness of 50 denier or less.

The present invention also provides a method for producing athermoplastic polyurethane yarn, comprising the steps of: compoundingthermoplastic polyurethane with silica nanopowder having a particle sizeof 30 nm or less to prepare a pellet-type master batch, and compoundingthe master batch with thermoplastic polyurethane to prepare a resin forproducing a yarn; and introducing the resin into a yarn extruder, andmelt-extruding the introduced resin, thereby producing a thermoplasticpolyurethane yarn having a thickness of 50 denier or less.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail. In the following detailed description, exemplaryembodiments of the present invention, which achieve the above-describedtechnical objects, will be presented. In addition, other embodiments ofthe present invention, which are not described herein, will be apparentfrom the following description.

In the present invention, unlike the inventions disclosed in theabove-described Patent documents, the surface of a polyester or nylonyarn is not coated with thermoplastic polyurethane. Specifically, in thepresent invention, thermoplastic polyurethane alone is compounded withsilica nanopowder having a particle size of 5-30 nm, which serves as athickener suitable for producing a yarn having a small thickness,preferably a thickness of 50 denier or less, so that the resulting resincan have desired processability and physical properties. Therefore, thepresent invention is intended to provide a resin for a thermoplasticpolyurethane resin, which comprises silica nanopowder, and a method forproducing a thermoplastic polyurethane yarn using the resin.

The present invention also provides a method capable of producing acore-free thermoplastic polyurethane yarn by compounding a silicananopowder-containing master batch with thermoplastic polyurethane andmelt-extruding the compound through a yarn extruder.

For this, the following requirements should be satisfied: 1) athermoplastic polyurethane (TPU) resin composition, which is used forproduction of a thermoplastic polyurethane yarn, and a method forpreparation of the composition, should be disclosed in detail; 2) amethod for preparation of a master batch for a thermoplasticpolyurethane yarn and the composition thereof should also be disclosedin detail; and 3) a method of producing a core-free thermoplasticpolyurethane yarn using the TPU resin or the master batch should bedisclosed in detail.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail.

Embodiment 1

The present invention is directed to a method of producing athermoplastic polyurethane (hereinafter also referred to as “TPU”) yarnfrom TPU alone without coating the surface of a polyester or nylon yarnwith TPU. Herein, the TPU yarn may be a mono-filament yarn or amulti-filament yarn.

Thermoplastic polyurethane that is used in the present invention isvirgin TPU. The virgin TPU is prepared by polymerizing polyester polyol,polyether polyol, polycarprolactone or the like with aromatic isocyanateor aliphatic isocyanate using short chain glycol (e.g., 1,4-butanediol)as a chain extender.

In the present invention, in addition to the virgin TPU, various TPUscraps, including a scrap remaining after high-frequency welding work ofTPU for footwear or a scrap remaining after hot-melt processing of TPU,may be used alone or in combination with virgin TPU.

In the present invention, a core-free TPU yarn is produced withoutcoating the surface of a polyester or nylon yarn with TPU. In thisproduction process, a thickener or an inorganic material (talc or CaCO3)having a thickening effect is used so that the TPU yarn will becontinuously extruded without being broken during an extrusion processto thereby increase the production of the yarn and so that theprocessability of the yarn will be improved.

In the present invention, silica powder is preferably used as athickener. The silica powder is added to a liquid raw material forsynthesis of TPU to prepare TPU resin. Alternatively, the silica powderis compounded with general TPU to prepare a master batch.

Particularly, in the present invention, a TPU resin prepared usingsilica nanopowder (preferably, silica nanopowder having a particle sizeof 5-30 nm), or a master batch prepared by compounding TPU with thesilica nanopowder, is used, because it is impossible to produce a TPUyarn having a small thickness of 50 denier or less when silica having ageneral particle size is used.

Specifically, in the present invention, silicon nanopowder having aparticle size of 5-30 nm is added to any one of liquid raw materialswhich comprise polyol, isocyanate and short-chain glycol, respectively,and which are used for preparation of TPU polymer pellets. The mixtureis stirred sufficiently and polymerized with the remaining two rawmaterials to form TPU polymer pellets, thereby preparing a resin for aTPU yarn. Herein, the content of the silica nanopowder is preferably 10wt % or less. If the silica nanopowder is added in an amount of morethan 10 wt %, there will be a disadvantage in that stirring isdifficult.

In addition, in the present invention, a resin for a TPU yarn may alsobe prepared by compounding silica nanopowder having a particle size of5-30 nm with general TPU to prepare a master batch and compounding TPUresin with a predetermined amount of the master batch. In the process ofcompounding silica powder TPU to prepare the master batch, the contentof the silica nanopowder is 40 wt % or less. If the silica nanopowder isused in an amount of more than 40 wt %, a problem will arise in that thesilica nanopowder is not compounded with TPU so that the master batchcannot be prepared and a TPU yarn cannot be produced. For this reason,when silica nanopowder having a particle size of 5-30 nm is to becompounded with TPU, the silica nanopowder is added in an amount of 40wt % or less. To prepare the most ideal master batch, the content of thesilica nanopowder is preferably 30 wt %.

Hereinafter, a detailed description will be made of 1) a method ofpreparing a resin for a TPU yarn by adding silica nanopowder to a liquidraw material for preparation of TPU, 2) a method of preparing a masterbatch by compounding silica nanopowder with TPU, and 3) a method ofproducing a core-free TPU yarn using the resin for the TPU yarn or themaster batch.

1. Method for Preparing Resin for TPU Resin According to the PresentInvention

The method for preparing the resin for the TPU yarn is a method ofpreparing a resin by adding silicon nanopowder to a liquid raw materialfor preparation of TPU polymer pellets and polymerizing the siliconnanopowder-containing liquid material. The method of preparing the resincomprises the following four steps.

-   -   Step 1: Liquid raw materials for preparation of TPU polymer        pellets are prepared. Specifically, polyol, isocyanate and        short-chain glycol are prepared.    -   Step 2: Any one is selected from among the liquid raw materials        prepared in step 1, and silica nanopowder having a particle size        of 5-30 nm is added and compounded into the selected liquid raw        material. Herein, the compounding is preferably performed at a        temperature of 80 to 100° C. and a stirring speed of 20-30 rpm.        For example, in the present invention, silica nanopowder is        mixed with polyol, followed by compounding.    -   Step 3: The silica powder-dispersed liquid raw material of step        2 and the remaining two raw materials are simultaneously        introduced into a reaction-type extruder to prepare TPU polymer        pellets.    -   Step 4: The TPU polymer pellets of step 3 are dried and aged,        thereby obtaining a resin for a TPU yarn according to an        embodiment of the present invention.

2. Method for Preparation of Master Batch According to the PresentInvention

-   -   Step 1: The above-described TPU (for example, virgin TPU, a TPU        scrap, or a mixture thereof) and silica nanopowder having a        particle size of about 30 nm or less (preferably 5-30 nm) are        prepared to have predetermined contents. Herein, the content of        the silica nanopowder is 40 wt % or less.    -   Step 2: The silica nanopowder and TPU are introduced into a        conventional kneader, and then compounded with each other at a        temperature of 100 to 120° C. and a speed of 20-30 rpm.    -   Step 3: The TPU compounded with the silica nanopowder is cooled,        crushed to a diameter of less than 10 mm, and then introduced        into a conventional twin extruder. Herein, the temperature of        the twin extruder is 150 to 200° C.    -   Step 4: The resin compounded in the twin extruder is pelletized        while it is passed through cooling water at 15 to 20° C.    -   Step 5: The master batch prepared through the above-described        steps 1 to 4, specifically a pellet-type master batch, is dried        and aged according to a conventional method.    -   Step 6: The master batch prepared as described above is        compounded with conventional TPU, thereby preparing a TPU resin        for yarn production.

3. Method for Producing TPU Yarn According to the Present Invention

A method for production of a TPU yarn, described in detail below, is amethod of producing a core-free TPU yarn without coating the surface ofa polyester or nylon yarn with TPU, unlike the inventions disclosed inthe prior art patent documents.

-   -   Step 1: Pellets for yarn production (specifically, (1) TPU resin        compounded with silica nanopowder, or (2) TPU resin prepared by        mixing and compounding the silica nanopowder-containing master        batch with TPU) are placed in a conventional yarn extruder and        melt-extruded at a temperature of 170 to 230° C. through the        extruder.    -   Step 2: Melt extrusion through the extruder, a TPU yarn released        through the dice of the extruder is cooled in cooling water at        25 to 40° C.    -   Step 3: The cooled yarn is drawn. In the present invention, the        cooled yarn is drawn about 7 or less. If the yarn is drawn 7        times or more, yarn breakage occurs.    -   Step 4: The drawn yarn is annealed in a conventional heating        chamber at a temperature of 150 to 160° C.    -   Step 5: The annealed yarn is wound, thereby producing a TPU yarn        having a thickness of 50 denier or less according to an        embodiment of the present invention. Specifically, when        polyester or nylon corresponding to the core of a TPU yarn is        not used, a TPU yarn having a thickness of 50 denier or less can        be produced without coating the surface of a polyester or nylon        yarn with TPU.

The above-described production method is a method of producing amono-filament yarn or a multi-filament yarn using a silicananopowder-containing thermoplastic polyurethane resin.

Meanwhile, in order to evaluate the physical properties of the TPU yarnproduced according to the above-described method, the physicalproperties of each of 1) TPU resin prepared using the silicananopowder-containing TPU resin and 2) TPU resin prepared using thesilica nanopowder-containing master batch were measured, and the resultsof the measurement are shown in Tables 1 and 2 below.

First, varying amounts of silica nanopowder were added to conventionalTPU, followed by to prepare TPU resins, and the physical properties ofthe prepared TPU resins were tested. The results of the test are shownin Table 1 below.

Specifically, in a process of preparing silica nanopowder-containing TPUresin according to the present invention, silica nanopowder was added toTPU in varying amounts of 0 phr, 3 phr, 5 phr, 7 phr and 10 phr, and theviscosity change, extrusion processability and surface state of theresin were observed during polymerization. Herein, as the TPU, polyesterpolyol-based TPU having a hardness of shore 75D was used.

TABLE 1 Content of silica nanopowder MFI in silica (230° C., Meltviscosity nanopowder- 2.16 kg) Tfb (Pa · s) containing Test grade (g/10min) (° C.) 230° C. 235° C. TPU resin T-75D-1 30.21 218.4 32620 10060  0phr T-75D-2 28.33 219.5 33480 11670  3 phr T-75D-3 25.42 220.6 3857013150  5 phr T-75D-4 18.25 221.3 42550 15090  7 phr T-75D-5 12.33 222.548080 17220 10 phr

In Table 1 above, T-75D-1, T-75D-2, T-75D-3, T-75D-4 and T-75D-5 setforth in “Test grade” are the trade names of TPU resins containingsilica nanopowder in amounts of 0 phr, 3 phr, 5 phr, 7 phr and 10 phr,respectively.

Referring to Table 1 above, the extrusion processabilities and surfacestates of TPU yarns will now be described.

When a TPU yarn was produced using the TPU resin (trade name: T-75D-1)without using the silica nanopowder-containing resin of the presentinvention, there were problems in that severe yarn breakage occurs dueto the excessively high flowability of the resin during extrusion and inthat the surface of the TPU yarn becomes rough.

When a TPU yarn was produced using the TPU resin containing 3 phr ofsilica nanopowder (trade name: T-75D-2) according to the presentinvention, the extrusion processability of the resin was good, no yarnbreakage occurred, and the yarn had a good surface.

When a TPU yarn was produced using the TPU resin containing 5 phr ofsilica nanopowder (trade name: T-75D-3) according to the presentinvention, the extrusion processability of the resin was good while yarnbreakage during extrusion did not occur and the TPU yarn had a goodsurface.

When a TPU yarn was produced using the TPU resin containing 7 phr ofsilica nanopowder (trade name: T-75D-4) according to the presentinvention, the resin showed a melt flow index of 18.25 g/10 min and aflow beginning temperature (Tfb) of 221.3° C., indicating that it hadgood extrusion processability. Furthermore, it showed melt flow indices(Pa·s) of 42550 at 230° C. and 15090 at 235° C., indicating that therewas no yarn breakage during extrusion. In addition, the TPU yarn had agood surface.

When a TPU yarn was produced using the TPU resin containing 10 phr ofsilica nanopowder (trade name: T-75D-5) according to the presentinvention, there was a disadvantage in that the TPU yarn had a slipperysurface.

The test results indicated that, in the process of producing the TPUyarn by adding silica nanopowder and performing polymerization, it ismost preferable to added the silica nanopowder in an amount of 3-7 phr.In addition, where the silica nanopowder was added in an amount of 10phr, there was difficulty in compounding the silica nanopowder with theliquid raw material.

Second, a test was performed using varying contents of a master batchcontaining the silica nanopowder compounded with conventional TPU, andthe results of the test are shown in Table 2 below.

Specifically, in the process of producing a TPU yarn by compoundingconventional TPU with a master batch (containing 30 wt % of silicananopowder) according to the present invention, the viscosity change,extrusion processability and surface state of the resin was observedwhile the master batch was compounded with the TPU in varying amounts of0 phr, 3 phr, 5 phr, 10 phr and 20 phr. Herein, as the TPU, polyesterpolyol-based TPU having a hardness of shore 75D was used.

TABLE 2 MFI Content (230° C., Melt viscosity of 2.16 kg) Tfb (Pa · s)master Test grade (g/10 min) (° C.) 230° C. 235° C. batch NS-75D-1 19.58215.2 35580 11010  0 phr NS-75D-2 16.83 216.3 31860 11450  3 phrNS-75D-3 14.32 218.2 40950 12830  5 phr NS-75D-4  8.35 222.3 44380 1403010 phr NS-75D-5  6.23 219.3 50570 16930 20 phr

In Table 2 above, NS-75D-1, NS-75D-2, NS-75D-3, NS-75D-4 and NS-75D-5set forth in “Test grade” are the trade names of TPU resins containingthe master batch in amounts of 0 phr, 3 phr, 5 phr, 10 phr and 20 phr,respectively.

Referring to Table 2 above, the extrusion processabilities and surfacestates of TPU yarns will now be described.

When a TPU resin was produced using the TPU resin containing no masterbatch (trade name: NS-75D-1), there were problems in that severe yarnbreakage occur due to the excessively high flowability of the resinduring extrusion and in that the surface of the TPU yarn becomes rough.

When a TPU yarn was produced using the TPU resin containing 3 phr of themaster batch (trade name: NS-75D-2) according to the present invention,the resin was easily flowable during extrusion, yarn breakage occurred,and the surface of the TPU yarn was slightly rough.

When a TPU yarn was produced using the TPU resin containing 5 phr of themaster batch (trade name: NS-75D-3) according to the present invention,the resin showed a melt flow index of 14.32 g/10 min and a flowbeginning temperature (Tfb) of 218.2° C., indicating that it had goodextrusion processability. Furthermore, the resin showed melt viscosities(Pa·s) of 40,950 at 230° C. and 12,830 at 235° C., indicating that therewas no yarn breakage during extrusion. In addition, the TPU yarn had agood surface.

When a TPU yarn was produced using the TPU resin containing 10 phr ofthe master batch (trade name: NS-75D-4) according to the presentinvention, the resin showed a melt flow index of 8.35 g/10 min and aflow beginning temperature (Tfb) of 222.3° C., indicating that it hadgood extrusion processability. Furthermore, the resin showed meltviscosities (Pa·s) of 44,380 at 230° C. and 14,030 at 235° C.,indicating that there was no yarn breakage during extrusion. Inaddition, the TPU yarn had a good surface.

When a TPU yarn was produced using the TPU resin containing 20 phr ofthe master batch (trade name: NS-75D-5) according to the presentinvention, the extrusion processability of the resin was good, and noyarn breakage occurred, but there was a disadvantage in that the TPUyarn had a slippery surface.

The above test results indicated that, in the process of producing theTPU yarn by compounding TPU with the master batch of the presentinvention, it is most preferable to add the master batch (containing 30wt % of silica nanopowder) in an amount of 5-10 phr. In addition, it wasseen that, when the master batch was added in an amount of 20 phr ormore, severe blooming in the TPU yarn appeared.

Meanwhile, Table 3 below shows a comparison of physical propertiesbetween a core-free TPU yarn produced using silica nanopowder and acore-free TPU yarn produced using general silica powder. Specifically,Table 3 below compares the physical properties of a TPU yarn producedusing silica nanopowder having a particle size of 5-30 nm with those ofa TPU yarn produced using silica powder having a particle size of300-500 nm.

TABLE 3 Comparison Use of general Use of silica items silica powdernanopowder Remarks TPU grade Core-free TPU Core-free Compounded with 10yarn resin TPU yarn phr of TPU containing (trade name: resin (trade 30wt % of general NS-75D-10) name: NS- silica powder or silica 75D-4)nanopowder Silica particle 300-500 nm 5-30 nm Silica powder product sizehaving a particle size of less than 5 nm is not currently available;yarn breakage could occur when a silica powder product having a particlesize of more than 30 nm was added. TPU MFI  7.3  8.35 230° C., 2.16 kgf(melt flow index) TPU Tfb 224.5 222.3 (flow beginning temp.) TPU tensile250 kgf/cm² 350 kgf/cm² Use of injected strength sample TPU tear 178kgf/cm 205 kgf/cm Use of injected Strength sample TPU specific 1.23-1.261.22-1.25 g/cc gravity TPU hardness 75 ± 3D 75 ± 3A Shore D TPU yarn 50denier 50 denier thickness TPU surface Very rough Good state ExtrusionDue to a large Good process- silica particle extrusion ability size,severe process- yarn breakage ability occurred without during TPUbreakage of yarn extrusion, TPU yarn making the extrusion processdifficult.

As can be seen in Table 3 above, when the core-free TPU yarn wasproduced using general silica powder (having a particle size of 300-500nm), there were problems in that the TPU yarn had a rough surface andthe extrusion processability of the resin was poor. Particularly, whenthe general silica powder was used, a TPU yarn having a small thicknessof less than 50 denier could not be produced.

On the contrary, when the core-free TPU yarn was produced using silicananopowder having a particle size of 5-30 nm, the TPU yarn had a goodsurface, no yarn breakage during extrusion occurred, and the TPU resinshowed good processability.

As described above, according to the present invention, it is possibleto produce a thermoplastic polyurethane yarn, which can exhibit theeffects of the thermoplastic polyurethane-coated yarn disclosed in theprior art patent documents and also has a small thickness of 50 denieror less.

Although the preferred embodiments of the present invention have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A core-free thermoplastic polyurethane yarnformed with a resin, wherein the resin comprises thermoplasticpolyurethane as a base polymer of the core-free thermoplasticpolyurethane yarn, and silica nanopowder mixed to the thermoplasticpolyurethane by melt extrusion, wherein the silica nanopowder has aparticle size of 5 to 30 nm, wherein the core-free thermoplasticpolyurethane yarn has a thickness of 50 denier or less.
 2. The core-freethermoplastic polyurethane yarn of claim 1, wherein the resin is formedin pellets.